Rapid methods for the detection of pathogens in a sample (e.g., food) have been limited by the need for at least one enrichment step, which facilitates bacterial growth to a detectable level (e.g., to about 106 colony forming units (cfu)/mL for ELISA detection methods). Current regulatory guidelines specify that a single cfu must be detected in a 25 gram sample of food. Available technologies cannot instantaneously detect a single bacterium in such a large sample. As a result, enrichment procedures are typically used to increase the number of microorganisms in the sample to facilitate detection.
Pathogens are typically injured during processing of products. That is, the pathogens may have undergone heating, freezing, contact with chemical additives, or mechanical processing steps which injure or debilitate the pathogens. Thus, resuscitation of the pathogens before detection is often required.
Because stressed microorganisms may be inhibited by selective agents that do not typically inhibit healthy microorganisms, a common technique for screening for the presence of pathogens involves the use of a series of media (i.e., nutrient fluid) transfers starting from the use of a non-selective enrichment medium, and then the use of a selective medium. The non-selective enrichment medium is usually employed to resuscitate potentially injured pathogens. Once the pathogens have been revived, a small quantity of the non-selective enrichment medium is then transferred into the selective medium. This technique, which is often defined by human work patterns and the growth patterns of the pathogens, generally takes several days to complete. Over the years, many attempts have been made to shorten the length of the primary enrichment step to reduce total assay time. Generally, it has been found that at least 8 to 24 hours of non-selective enrichment is required to obtain sufficient viable pathogens for further testing.
Detection methods involving pre-enrichment and selective enrichment steps are laborious and, because of their complexity, can be subject to a variety of human errors that may affect the result. A need exists for simpler enrichment procedures to obtain larger quantities of target microorganisms, or detectable biomolecule components thereof, in a sample.